Carbon nanoparticles are common knowledge. One form in which carbon nanoparticles may be present is that of carbon nanotubes.
One problem that these carbon nanoparticles or nanotubes have is their insolubility. Moreover, the production of carbon nanoparticles or nanotubes forms by-products (amorphous carbon, nm-size metal particles) which have to be removed when the intention is to use the nanoparticles or nanotubes, for example, in nanoelectronics.
Carbon nanotubes have very small cylindrical structures with a diameter of a few nanometers and a length ratio of from 10 to 1000. Carbon nanotubes have a honeycomb-like hexagonal structure in which each carbon atom is bonded to three adjacent carbon atoms. Depending on their exact structure, carbon nanotubes can act as conductors or as semiconductors. Carbon nanotubes may be present, for example, in the form of “single-wall carbon nanotubes”, (SWNTs) and are then referred to in general terms as “buckytubes”. For the sake of simplicity, these carbon nanotubes will also be referred to hereinafter as SWNTs. Owing to their unique properties, these SWNTs are the subject of intensive research studies. The properties of the SWNTs include strength/durability, stiffness, very high Young modulus, and thermal and electrical conductivity. SWNTs are similar to the fullerenes, which consist essentially of sp2-hybridized carbon atoms which are typically arranged in pentagons or hexagons (see, for example, B. I. Yakobsen and R. E. Smalley, American Scientist, Vol. 85, July-August, 1997, 324-337).
They can be prepared in relatively large amounts and in reproducible quality by controlled catalyzed growth initiated by metal nanoparticles.
“As-prepared” SWNTs, i.e. those which are yet to be processed after the preparation, tend to aggregate owing to the large surface pi systems and are therefore insoluble, difficult to free from the catalyst nanoparticles by purification, and generally not amenable to chemical reactions which require a homogeneous phase. The catalyst nanoparticles still present in the “as-prepared SWNTs” prevent, for example, use in nanocircuits. “As-prepared” SWNTs may still contain unshaped nanoparticles, i.e. those which are not of precisely defined shape, in an amount of up to 50% by weight of impurities (according to the catalyst). It would therefore be desirable to chemically derivatize carbon allotropes, particularly carbon nanoparticles, especially carbon nanoparticles comprising or consisting of carbon nanotubes, such that they are soluble in a common organic solvent.
It would thus be possible to free the “as-prepared” SWNTs of catalyst residues by purification. Carbon nanotubes may additionally also be present in the form of “multi-wall carbon nanotubes” (MWNTs). MWNTs are concentric SWNTs and have properties which are similar to those of the SWNTs but inferior. SWNTs have fewer defects compared to MWNTs and are accordingly stronger and more durable and have a higher conductivity.
Whether a particular carbon nanotube is metallically conductive, semiconductive or nonconductive is determined by factors including its chirality.
Subdivision is equally possible according to the diameter, SWNTs having diameters of from 0.7 to 3 nm and MWNTs a diameter of from 2 to 20 nm.